Many digital cameras are currently equipped with a zoom lens and a single image sensor to photograph still images and moving images. A photographed image is digitally processed to generate a digital image file, and the generated digital image file is stored in a memory in the digital camera. The digital image file is next transferred to a computer to be displayed thereon, or is transferred to a printer to be printed.
Preferable specifications for a digital camera are to be small in size and large in optical zoom range. A user prefers a large zoom range to a limited zoom range. However, when a digital camera is equipped with a large zoom range lens without sacrificing image quality of a photographed image, the digital camera increases in size. In an expensive camera such as an optical single-lens reflex camera, it is possible to use a plurality of interchangeable lenses such as a 28 mm-70 mm zoom lens and a 70 mm-210 mm zoom lens. However, such interchangeable lenses are inconvenient for a user using a compact digital camera.
Some digital cameras use a single lens and a plurality of image sensors for generating a color image. Light from a subject is split by a prism beam splitter into a plurality of colors to be used for a plurality of monochrome image sensors to image R, G and B color images.
Moreover, conventionally, a stereo film camera and a stereo digital camera have been also known. These cameras have two lenses having the same focal distance and being arranged separately in the horizontal direction, and form two images of scenes that slightly differ from each other, in two frames of a film or two imaging sensors. The two images constitute the so-called stereo pair. The two lenses are designed to have the same magnifying power, and are used simultaneously in order to form, on the image sensors, the images for the left eye and the right eye for obtaining a stereo effect.
In a compact digital camera, in order to obtain a large zoom range without taking any time for interchanging lenses, it is suitable to mount a plurality of lenses having different focal distances to use them appropriately according to zoom positions. However, for example, in the case where two lenses having different focal distances are mounted in a camera, how each focal distance is set and how the two lenses are changed become important. A digital camera can have both an optical zoom function, and an electronic zoom function which can electronically zoom the digital image data.
Moreover, in a digital camera, when the optical zoom function can provide a zoom position which a user has set, only the optical zoom is executed; in contrast, when the optical zoom function is insufficient, the electronic zoom is executed to a distance beyond the maximum focal distance of the optical zoom. However, in the case where the optical zoom is driven stepwise or discretely, using the electronic zoom function to interpolate within the gaps between the zoom positions obtained by the optical zoom has been proposed.
Japanese Patent Laid-Open Publication No. Hei 10-42183 states that a camera equipped with a single lens and a single image sensor drives the electronic zoom and the optical zoom to determine an angle of view, and increases the ratio of the optical zoom while maintaining the angle of view.
Moreover, in relation to a camera equipped with an optical viewfinder and a zoom viewfinder, Japanese Patent Laid-Open Publication No. 2003-283910 states that these viewfinders are suitably changed, and that the lens of the optical viewfinder system is driven in the state of being interlocked with the taking lens in order to ensure that the angle of view of the optical view finder coincides with that of the electronic viewfinder at the time of a change from the electronic viewfinder to the optical viewfinder.
Moreover, Japanese Patent Laid-Open Publication No. Hei 8-18842 states that in the case where the optical power of a multifocal lens is changed discontinuously, the electric zoom power is controlled so as to interpolate to obtain optical power other than that which is changed by the multifocal lens, and thereby zoom power is continuously changed in a manner similar to that in the case where a zoom lens is used.
All of the above-mentioned conventional techniques pertain to cameras each equipped with a single lens and a single image sensor, and do not pertain to a camera system equipped with a plurality of optical systems for photographing a scene. Consequently, the conventional techniques do not naturally teach how to change a plurality of optical systems.
A digital camera equipped with a fixed focal distance lens and a zoom lens as two lenses will now be considered. Settings of these two lenses are presumably changed as follows. That is, the focal distance gap between the focal distance of the fixed focal distance lens and the minimum focal distance of the zoom lens is interpolated by the electronic zoom of a digital image obtained by the fixed focal distance lens. Zoom setting means (a zoom button) for setting a zoom position is mounted on the camera, and a user can take a photograph in a desired zoom position by setting the zoom setting means to a wide setting or a telephoto setting. When the user sets the zoom setting means mounted on the camera to “telephoto,” a digital image obtained by the fixed focal distance lens is electronically zoomed in. When the electronic zoom reaches the telescopic end of the electronic zoom, the electronic zoom is changed to the zoom lens for subsequent optical zooming. Moreover, when the user operates the zoom setting means and sets it to “wide,” optical zoom-out of the digital image obtained by the zoom lens is performed. When the optical zoom down has reached the minimum focal distance of the zoom lens, the optical zoom-out is changed to the electronic zoom of the fixed focal distance lens, and subsequently the zoom-out of the fixed focal distance lens is performed.
An overlapping range can also be formed by extending the electronic zoom range of the fixed focal distance lens to the optical zoom range of the zoom lens, and either the electronic zoom or the optical zoom can be selected in the overlapping range. Because the electronic zoom is to perform the interpolation processing in order to extend a digital image obtained with an imaging device such as a CCD device or a CMOS device, the electronic zoom has a problem of deterioration in the image quality of the digital image. For this reason, using the optical zoom in the overlapping range is generally preferable. However, because the zoom power obtained by the optical zoom is discretely located when the optical zoom is driven discontinuously; i.e. stepwise, interpolation has to be performed by the electronic zoom between the discrete zoom positions of the optical zoom, which causes deterioration in image quality.